Synthesis of a Hydroxyl-Containing Corrosion Inhibitor and Its Inhibitory Performance on N80 Steel in Hydrochloric Acid Solution
Round 1
Reviewer 1 Report
1. Characterization is incomplte and additional evidence of the formed product is required to guarantee structure (NMR) and purity (HPLC, GCMS)
2. The article does not specify if the corrosion inhibition comes from an organic layer at the steel/acid interface or if there is a chemical reaction that binds steel/MY materials.
3. Figure 6 caption is not clear
4. It would be desirable to have a references of a known corrosion inhibition agent for comparison.
5. Proposed inhibition mechanisms should be explained with more detail and with a proposal of the chemical interaction taking place.
6. As there is no evidence of the formation of the proposed molecule (other than FTIR), the inhibitory effect of main precursor (acetophenone) should be tested in order to discard any false positive inhibitory effec wrongly attributed to a molecule that has not been fully identified.
Author Response
Please see the attachment.
Point 1: Characterization is incomplte and additional evidence of the formed product is required to guarantee structure (NMR) and purity (HPLC, GCMS).
Response 1: Thank you very much for your careful review and constructive suggestions. The GCMS has been added to the latest version of this manuscript to provide more evidence for the structure of the target product, as detailed in lines 172-178 of the manuscript.
Point 2: The article does not specify if the corrosion inhibition comes from an organic layer at the steel/acid interface or if there is a chemical reaction that binds steel/MY materials.
Response 2: We thank the reviewer for raising this question. Through fitting, it is concluded that both MY1 and MY2 meet the Langmuir adsorption isotherm model, indicating that the adsorption of these two corrosion inhibitors on steel surface belongs to single-layer adsorption. At this point, the probability of corrosion inhibitor adsorption on the metal surface is the same. The Gibbs free energy (∆G) describing the interaction between adsorbed molecules and metal surface can be calculated by the Langmuir adsorption isotherm equation. If ∆G is negative, it indicates that the corrosion inhibitor is spontaneously adsorbed on the metal surface. If the |∆G|≤20kJ/mol, the adsorption mode of the corrosion inhibitor is mainly physisorption type; If the |∆G|≥40kJ/mol, the adsorption mode of the corrosion inhibitor is mainly chemisorption type（Such as Flores, E.A.; Olivares, O.; Likhanova, N.V.; Domínguez-Aguilar, M.A.; Nava, N.; Guzman-Lucero, D.; Corrales, M. Sodium phthalamates as corrosion inhibitors for carbon steel in aqueous hydrochloric acid solution. Corrosion Science 2011, 53, 3899-3913）.It can be seen from Tab.4 in the manuscript that MY1 and MY2 are mixed adsorption types with both physisorption type and chemisorption type. When the inhibitor is added, the inhibitor ions generate electrostatic attraction with the charge on the metal surface, and the N atoms containing lone pair electrons form coordination bonds with the iron atoms on the metal surface. Thus, the adsorption film layer is formed to block the metal from the corrosive medium, so as to achieve the effect of corrosion inhibition.
Point 3: Figure 6 caption is not clear.
Response 3: We are so grateful for your kind question. Figure 6 has been revised in the manuscript, and EDS elemental mapping images have been added. For details, see lines 288-289 of the manuscript.
Point 4: It would be desirable to have a references of a known corrosion inhibition agent for comparison.
Response 4: We thank the reviewer for raising this question. The following figure shows the Nyquist diagrams of two commonly used corrosion inhibitors, JH-1 (containing amino-trimethylphosphonic acid), JH-2 (containing polyepoxysuccinic acid), and MY1 and MY2 in the manuscript at 0.7% (mass fraction) concentration. It can be seen from the Nyquist diagram that these four corrosion inhibitors have corrosion inhibition effect, but the corrosion inhibition effect MY1 > MY2 > JH-2 > JH-1.
Point 5: Proposed inhibition mechanisms should be explained with more detail and with a proposal of the chemical interaction taking place.
Response 5: We are so grateful for your kind question. The experiment shows that MY1 and MY2 have an inhibition effect on the metal surface in 15% hydrochloric acid solution. Through the Gibbs Free energy (∆G) and Langmuir adsorption isothermal model, it is found that MY1 and MY2 belong to the mixed adsorption that both physical adsorption and chemical adsorption exist. The existence of physical adsorption is due to the existence of polar and non-polar groups in the corrosion inhibitor molecules. When the polar groups of the corrosion inhibitor molecules are absorbed on the metal surface, the non-polar groups are closely arranged under the action of van der Waals force, thus forming a firm adsorption film. At the same time, benzene ring can be adsorbed on the metal surface through conjugation to enhance the stability of adsorption (Such as Senthilkumar, A.; Tharini, K.; Sethuraman, M. Studies on a few substituted piperidin-4-one oximes as corrosion inhibitor for mild steel in HCl. Journal of materials engineering and performance 2011, 20, 969-977). Chemical adsorption is due to the fact that MY1 and MY2 contain multiple N and O atoms that can provide lone pair electrons, and they can form coordination bonds with iron atoms (Such as Quraishi, M.A. 2-Amino-3, 5-dicarbonitrile-6-thio-pyridines: new and effective corrosion inhibitors for mild steel in 1 M HCl. Industrial & Engineering Chemistry Research 2014, 53, 2851-2859). Such chemical bonds have strong chemical forces, which enable the corrosion inhibitor molecules to be firmly adsorbed on the metal surface and prevent the diffusion of chloride of ions and hydrogen ions to the interior of the metal. It is precisely because of the existence of mixed adsorption, on the one hand, the charge state and interface properties of the metal surface are changed, the energy of the metal surface becomes stable, the activation energy of the corrosion reaction is increased, and the corrosion rate is slowed down. On the other hand, the non-polar group separates the metal surface from the corrosive medium, hindering the charge transfer in the electrochemical reaction and thus slowing the corrosion. In addition, the hydroxyl group contained in MY1 can improve the dispersion of corrosion inhibitor in 15% hydrochloric acid solution, and it is easier to form a dense adsorption film on the metal surface, improving the corrosion inhibition effect. After the addition of corrosion inhibitor, the wetting angle of steel surface increases significantly, indicating that the adsorption film formed by corrosion inhibitor molecules on steel surface increases the hydrophobicity and inhibits corrosion. For details, see lines 375-399 of the manuscript.
Point 6: As there is no evidence of the formation of the proposed molecule (other than FTIR), the inhibitory effect of main precursor (acetophenone) should be tested in order to discard any false positive inhibitory effec wrongly attributed to a molecule that has not been fully identified.
Response 6: Thank you very much for your careful review and constructive suggestions. The following figure shows Nyquist diagrams in 15% hydrochloric acid solution with 0.7% MY1,MY2,acetophenone, and formaldehyde. As can be seen from the figure, although the addition of formaldehyde and acetophenone increased the arc of the capacitive reactance compared with the blank experiment, the arc of the capacitive reactance increased significantly after the addition of MY1 and MY2. It shows that MY1 and MY2 have obvious inhibition effect, and there is no false positive.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Authors presented valuable data on compounds promising for the protection of metal surfaces from damage caused by acid. Compounds MY1 and MY2 surpass previously published organic inhibitors in inhibition efficiency. Inhibition characteristics are described thoroughly. Attempts to explain the inhibition mechanism are made, in particular, “the benzene ring can be adsorbed on the metal surface through conjugation to form a hydrophobic protective film” and “multiple N and O atoms can provide lone pair electrons, which can form coordination bonds with iron”.
The manuscript can be accepted after minor revision. Some comments:
- Structures of previously studied corrosion inhibitors mentioned in the lines 57 and 60, 454 and 456 should be given in the separate Figure.
- It is unclear, were compounds MY1 and MY2 reported somewhere in the literature. If yes, authors should add the reference. If not, they should give full chemical names: 3-(2-hydroxyethylamino)-1-phenylpropan-1-one and 3-(2-aminoethylamino)-1-phenylpropan-1-one.
- Mass spectrometry data and IR spectra data should be given in the Experimental part additional to their discussion in the chapter 3.1.
- If compounds MY1 and MY2 are novel, NMR 1H spectra should be recorded, melting points and elemental analysis data are necessary in experimental part.
Author Response
Please see the attachment.
Point 1: Structures of previously studied corrosion inhibitors mentioned in the lines 57 and 60, 454 and 456 should be given in the separate Figure.
Response 1: Thank you very much for your careful review and constructive suggestions. The following figure shows the structural formula of corrosion inhibitor previously study mentioned in the manuscript. Because these structures are different from those we studied, and they may be somewhat abrupt when they are put in the manuscript, so they are not put in the manuscript.
Point 2: It is unclear, were compounds MY1 and MY2 reported somewhere in the literature. If yes, authors should add the reference. If not, they should give full chemical names: 3-(2-hydroxyethylamino)-1-phenylpropan-1-one and 3-(2-aminoethylamino)-1-phenylpropan-1-one.
Response 2: We thank the reviewer for raising this question. We have given the chemical name in the latest manuscript. The details are in lines 103-105 of the manuscript.
Point 3: Mass spectrometry data and IR spectra data should be given in the Experimental part additional to their discussion in the chapter 3.1.
Response 3: We thank the reviewer for raising this question. We have supplemented the mass spectrometry data and IR spectra data in the experimental part. The details are in lines 106-110 of the manuscript.
Point 4: If compounds MY1 and MY2 are novel, NMR 1H spectra should be recorded, melting points and elemental analysis data are necessary in experimental part.
Response 4: Thank you very much for your careful review and constructive suggestions. We can confirm that the synthetic material conforms to the target product through the mass spectrometry data and IR spectra data. We mainly want to study the corrosion inhibition mechanism after the inhibitor is added, so we did not do much chemical structure element analysis.
Author Response File: Author Response.pdf
Reviewer 3 Report
Dear Editor,
Hope all the best for you, your co-workers in editorial office and honorable authors. I revised the manuscript "Synthesis of a Hydroxyl-Containing Corrosion Inhibitor and 2 Its Inhibitory Performance on N80 Steel in Hydrochloric Acid 3 Solution". The work is very good and a novel idea has illustrated.
1. The work is well designed and described.
2. The results are clearly presented and well interpreted.
3. Introduction needs to be greatly improved. it does not reflect the novelty of the work.
4. The Abstract part needs to write the innovation of the work.
5. In the conclusion part, the experimental results should be more fully summarized.
Comments for author File: Comments.pdf
Author Response
Please see the attachment.
Point 3: Introduction needs to be greatly improved. it does not reflect the novelty of the work.
Response 3: Thank you very much for your careful review and constructive suggestions. In the latest manuscript, the research content of this paper is narrated. The inhibition mechanism of two kinds of corrosion inhibitors with different configurations and the influence of the solubility of corrosion inhibitors on the inhibition efficiency are emphasized. The details are in lines 75-84 of the manuscript.
Point 4: The Abstract part needs to write the innovation of the work.
Response 4: We thank the reviewer for raising this question. In the abstract of this manuscript, the purpose of introducing polar groups is added, the intention is to improve the solubility of the corrosion inhibitor itself by introducing polar groups, and then improve the corrosion inhibition efficiency. The details are in lines 14-18 of the manuscript.
Point 5: In the conclusion part, the experimental results should be more fully summarized.
Response 5: We thank the reviewer for raising this question. By means of static weight loss test method and electrochemical method, this manuscript shows that both of the two corrosion inhibitors have corrosive effects, and belong to the mixed corrosion inhibitor based on inhibiting anode. SEM, EDS mapping and contact angle experiments showed that after the addition of corrosion inhibitors, the molecules of corrosion inhibitors formed a dense hydrophobic film on the metal surface, which hindered the contact between the metal surface and the corrosive medium. Through the corrosion inhibitor dispersion experiment, it is verified that the solubility of corrosion inhibitor itself has an effect on the corrosion inhibition efficiency. The details are in lines 414-427 of the manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have modified the manuscript, still, there are some issues to be addressed:
GC-MS studies are only superficial and no chromatogram ins presented to know the full composition of the system
Figures have different styles and are hard to understand. Also, microscopy analysis and discussion need to be improved. I consider the appear could be published under major corrections.
Author Response
Please see the attachment
Point 1: GC-MS studies are only superficial and no chromatogram ins presented to know the full composition of the system.
Response 1: Thank you very much for your careful review and constructive suggestions. The scanning mode used in the mass spectromrtry test process to characterize the product. The original data file was processed by PeakView as shown in the figure below. Combined with the mass charge ratio of the target product and the predicted structure of the fragmented ions. It can be seen from the relevant structure of the FTIR that the target product has been successfully synthesized. In addition, the mass spectrometry data has been replotted to maintain a consistent picture style. The details are in lines 182-184 of the manuscript.
Point 2: Figures have different styles and are hard to understand. Also, microscopy analysis and discussion need to be improved.
Response 2: We thank the reviewer for raising this question. We have recalibrated the format of the pictures in the manuscript. The title of Figure 6 has been changed, and the microscope analysis and discussion section has also been described in detail. Figure 7 and Figure 8 in the manuscript do not insert error bars because R2 (Fitting error coefficient) obtained by fitting is consistent with the trend of the data. Secondly, the error bars are not obvious in the figure after insertion, and the dispersion of the data is very small. Therefore, the figure with error bars is not included in the manuscript. The figure below shows Figure 7 and Figure 8 with error bars (green means error bars). The details are in lines 260-287 of the manuscript.
Author Response File: 
Author Response.docx
